gh-104146: Remove unused attr 'parameter_indent' from clinic.DLParser (#106358)

Author: erlend-aasland

Diff for: Tools/clinic/clinic.py

@@ -4326,7 +4326,6 @@ def __init__(self, clinic: Clinic) -> None:
     def reset(self) -> None:
         self.function = None
         self.state = self.state_dsl_start
-        self.parameter_indent = None
         self.keyword_only = False
         self.positional_only = False
         self.group = 0